1. Field of the Invention
The present invention relates to network systems, and more particularly, to offloading host system operating tasks for managing network related operations.
2. Background of the Invention
Computer networks are commonly used today in various applications. Computer networks typically use a layered protocol structure to manage network traffic. One common model that is typically used is the ISO model that includes a physical layer, a data link layer that includes a MAC layer, a network layer and others.
Various protocols/standards are currently used by computing systems and devices to communicate via networks. The following provides an introduction of some of the standards/protocols:
Transmission Control Procotol/Internet Protocol (“TPC/IP”): TCP is a standard network protocol (incorporated herein by reference in its entirety) that provides connection-oriented, reliable, byte stream service. This means that two nodes establish a logical connection before sending data and that TCP maintains state information regarding the data transfer. Reliable means that data is delivered in the same order that it was sent. A byte stream service means that TCP views data to be sent as a continuous data stream that is sent in any way it sees fit and delivers it to the remote node as a byte stream.
The IP standard protocol (incorporated herein by reference in its entirety) provides a datagram service whose function is to enable routing of data through various network subnets. Each of these subnets could be a different physical link such as Ethernet, ATM, etc. IP is also responsible for fragmentation of the transmit data to match a local link's MTU. IP can fragment data at the source node or at any intervening router between the source and destination node.
A complete description of the TCP/IP protocol suite is provided in “TCP/IP” Illustrated, Vol. 1 by W. Richard Stevens and Volume 2 by Gary R. Wright and W. Richard Stevens published by Addison Wesley Professional Computing Series that is incorporated herein by reference in its entirety.
iSCSI Protocol: Internet SCSI (iSCSI) as defined by the Internet Engineering Task Force (IETF) maps the standard SCSI protocol on top of the TCP/IP protocol. iSCSI (incorporated herein by reference in its entirety) is based on Small Computer Systems Interface (“SCSI”), which enables host computer systems to perform block data input/output (“I/O”) operations with a variety of peripheral devices including disk and tape devices, optical storage devices, as well as printers and scanners. The iSCSI and TCP/IP protocol suite consist of 4 protocol layers; the application layer (of which iSCSI is one application), the transport layer (TCP), the network layer (IP) and the link layer (i.e. Ethernet).
A traditional SCSI connection between a host system and peripheral device is through parallel cabling and is limited by distance and device support constraints. For storage applications, iSCSI was developed to take advantage of network architectures based on Ethernet standards. iSCSI leverages the SCSI protocol over established networked infrastructures and defines the means for enabling block storage applications over TCP.
The iSCSI architecture is based on a client/server model. Typically, the client is a host system such as a file server that issues a read or write command. The server may be a disk array that responds to the client request. Typically the client is an initiator that initiates a read or write command and a disk array is a target that accepts a read or write command and performs the requested operation.
In a typical iSCSI exchange, an initiator sends a “read” or “write” command to a target. For a read operation, the target sends the requested data to the initiator. For a write command, the target sends a “Ready to Transfer Protocol Data Unit (“PDU”)” informing the initiator that the target is ready to accept the write data. The initiator then sends the write data to the target. Once the data is transferred, the exchange enters the response phase. The target then sends a response PDU to the initiator with the status of the operation. Once the initiator receives this response, the exchange is complete. The use of TCP guarantees the delivery of the PDUs.
Typically, logical units in the target process commands. Commands are sent by the host system in Command Descriptor Blocks (“CDB”). A CDB is sent to a specific logical unit, for example, the CDB may include a command to read a specific number of data blocks. The target's logical unit transfers the requested data block to the initiator, terminating with a status message indicating completion of the request. iSCSI encapsulates CDB transactions between initiators and targets over TCP/IP networks.
There has been a need to offload TCP/IP protocol stack processing from a host computer system to a network adapter. A network adapter that executes the TCP/IP protocol stack is called a TOE (TCP Offload Engine).
Most TOE devices provide a single physical interface to a host processor (“CPU”). Applications that run on the host side are allocated memory locations. In most environments (for example, Windows®, Linux and others) the memory locations on the host side used to access the TOE interface is controlled by the operating system. This is inefficient because the operating system context to receive and send data on behalf of the application is different from the context of the application. Hence, context switching between the application and the operating system is used by conventional systems to process network traffic. This can result in latencies and network bandwidth degradation and hence is undesirable.
Therefore there is a need for a system and method that will allow plural applications running on a host system to efficiently access an adapter to communicate with a network.